Such a gear system as mentioned above includes a lubricating oil supply port and a lubricating oil outlet port for use in lubricating and cooling down the gears. The lubricating oil supply port is used for spraying lubricating oil onto the gears, and the lubricating oil outlet port is used for collecting, with an oil scavenging pump, the lubricating oil that has been used for lubricating and cooling down the gears. Power loss in such a gear system is mainly caused by air resistance and lubricating oil agitation resistance, which occur when the gears rotate. Particularly in the case of an aircraft engine, the gear train rotates at a relatively high speed, and therefore, air resistance due to the rotation of the gears is great. Moreover, in aircrafts developed in recent years, electrification of various airframe facilities has been promoted rapidly. Therefore, in the near future, a necessary power generation capacity is expected to increase greatly. In this case, power loss in a gear system that is caused by the air resistance and the lubricating oil agitation resistance also increases, which results in an increase in negative influence on the fuel consumption of an aircraft engine such as a jet engine or a gas turbine engine.
For the purpose of reducing the above-described power loss in a gear system, there is a proposed gear shrouding system (see Patent Literature 1) in which a plurality of gears meshing with each other in a gear train are covered by a shroud, so that a swirling air flow, which tends to be generated near front-end and rear-end faces of each gear when air is dragged by these faces of each gear due to rotation of the gears, is suppressed and thereby the air resistance is reduced. The shroud includes: a pair of side walls disposed opposite to the sides of each gear and in close proximity to the radially outer face of each gear; and an end wall disposed perpendicular to the pair of side walls and parallel to both of the front-end and rear-end faces of each gear. The shroud is provided such that the side walls and the end wall enclose both of the front-end and rear-end faces of each of the plurality of gears of the gear train. The end wall of the shroud is provided with an injection nozzle for injecting lubricating oil onto the gears and a second port for discharging the lubricating oil from the shroud. The shrouding system is capable of reducing air resistance due to rotation of the gears since the shroud, which is disposed in close proximity to the teeth of the gears, suppresses the above-described swirling air flow generated near both of the front-end and rear-end faces of each gear.